Nonvolatile semiconductor memories such as flash memories are used, as semiconductor storage, in various electronic apparatuses.
In any flash memory, a voltage of about 10 to 20 V is applied to the gate electrodes of the memory cell transistors to write data. To generate a high voltage of 10 V or more, a so-called “charge pump circuit” is arranged in a peripheral circuit of the flash memory.
The charge pump circuit comprises, for example, a plurality of MOS transistors and a plurality of capacitors. Each MOS transistor has its drain connected to the gate of another MOS transistor. The capacitors of the charge pump circuit are, for example, MOS capacitors. Each MOS capacitor is provided in one semiconductor region (element region) that is surrounded by an isolation region.
The charge pump circuit needs to have a plurality of MOS transistor groups and a plurality of MOS capacitor groups, in order raise the power-supply voltage (about 3 V) to about 20 V. The charge pump circuit therefore occupies a large area. Inevitably, the area the charge pump circuit occupies tends to increase.
As a result of this, the area for the memory cell array and the area for the peripheral circuit inevitably are limited. This makes it difficult to increase the storage capacity of the flash memory, to reduce the memory chip size and to lower the bit cost.